Seminar: “Nano-mechanical Characterization of Polypropylene and Nylon Fibers Exposed to Ultraviolet and Thermal Degradation”

BROWN UNIVERSITY
Joint Materials/Solid Mechanics Seminar Series

“Nano-mechanical Characterization of Polypropylene and Nylon Fibers Exposed to Ultraviolet and Thermal Degradation”

Prof. Vijay Chalivendra, co-Director for Biomedical Engineering and Biotechnology
Department of Mechanical Engineering
University of Massachusetts, Dartmouth

Abstract:
Nanoindentation studies using atomic force microscopy (AFM) was conducted to investigate the effect of accelerated ultraviolet (UV) and thermal degradation on mechanical properties of polypropylene (PP) and nylon fibers. The effect of degradation on gradation of Young’s modulus values across fiber cross-section was investigated with progressive nanoindentation from the surface to the center of the fiber. For polypropylene, UV degradation initially increases the Young’s modulus values both at the center and at the surface of the fibers until 120 hours of exposure and the values are decreased at 144 hours of exposure. The Young’s modulus values at 144 hours of exposure were less than those of unexposed PP fibers. For nylon, UV degradation decreases the Young’s modulus values from center to surface of the fibers up to 144 hours of exposure. Reduction of Young’s modulus at surface was greater than the center implying more deterioration at the surface. Wide angle x-ray spectroscopy (WAXS) analysis provided the increase of crystallinity in PP fibers exposed up to 120 hours and total destruction of crystallinity at 144 hours. Infrared spectra showed the oxidation by formation of carbonyl bonds with UV exposure. For nylon, WAXS showed continuous destruction of crystallinity. To investigate the thermal degradation effect, the PP and nylon fibers were exposed to 125oC and 175oC respectively for four weeks. Polypropylene did not show much impact on variation of Young’s modulus values initially, but showed an increase near the surface after four weeks exposure. Nylon fiber showed decrease in Young’s modulus. The changes in Young’s modulus values in both PP and nylon for UV and thermal degradation are again attributed to the changes of crystallinity. Polypropylene fibers are treated with a reducing agent to mitigate the oxidation and further characterization is in progress to evaluate the effect of treatment on mechanical properties of treated fibers.

Monday, March 29, 2010 - 4:00-5:00 pm - B&H Room 190